1. Field of the Invention
The present invention relates to printing heads for a dot line printer, and more particularly to complete assembly units of the printing heads in small sizes and light weight.
2. Description of the Prior Art
There has been a well-known dot line printer which can print characters, numerals and other symbols on printing paper by congregating a plurality of dots, and this dot line printer has been in wide use for the printer adopted in the data processing devices in the recent years, since all of the letters and the shapes can be optionally constructed by the combination of dots in this printer.
In order to increase the printing speed of the dot printer of this kind, it is required that the printing heads carrying printing wires move at a high speed to a line or a column direction with regard to a platen and printing paper, although such a moving speed is naturally limited by the response of magnetic actuators which drive the printing wires, and the other elements. In the prior art device, in order to enable the high speed printing, a plurality of printing wires were arranged in line with regard to the platen and driven in groups at the same time in accordance with the respective printing commands. This kind of printer is known as a dot line printer.
It is preferable in such a dot line printer to arrange in line the printing wires to provide all of the dots required to print one line. This arrangement requires such a wide space that the required number of the magnetic actuators cannot be actually positioned, and it is impossible to realize such a device cost effectively.
Because of this, such a device has been utilized that there are arranged in line the numbers of the printing wires corresponding to the dot positions of the numbers selected from all of the necessary dot numbers and that the frame wires carrying the printing wires are reciprocally driven only between the adjacent printing wire positions to provide false simultaneous printing. This device is known as a shuttle printer.
The shuttle type dot printer in the prior art is composed of the structure in which a plurality of printing wires and electromagnetic actuators are arranged in line and fixed to the shuttle frame, as is shown in the Japanese patent laying-open No. 59-131470 for example.
In this prior art device, such an improved dot line printer is provided that there is provided a permanent magnet to provide the urging force to the printing wire to make the light weight printing head is light in weight, which also makes the remarkably light in weight shuttle itself, and that also makes it not necessary to provide a balance weight for the shuttle drive.
In the prior art device mentioned above, however, the printing heads arranged in line on the shuttle frame are separated into the electromagnetic actuators and the printing springs which carry the printing wires respectively. As each of the electromagnetic actuator and the printing spring is separately fixed on the frame, each portion is still not lightened to the satisfactory degree and the printing heads have been limited their numbers to be attached to the shuttle frame. Thus, the high speed printing operation cannot be obtained by the device substantially small sized as practically requested.
Moreover, in the prior art device mentioned above, since the parts must be individually attached to the shuttle frame by screws or the like one by one and also must be individually adjusted at every assembling stage one after another, the efficiency in the assembly line is remarkably lowered. Especially, as the numbers of the printing wire to be assembled to the shuttle frame are increased, the unadjustment of only one printing wire prevents the other numbers of the printing wire block having no problem from proceeding to the next stage, and the efficiency is also extremely lowered in a practical production process.
Furthermore, in the prior art device, for the exchange of the worn-out printing wire, the inspection and the maintenance of the actuators, etc. every part must be individually maintained and a great deal of labor must be provided by skilled workers.
In order to solve such problems mentioned above it is preferable to unitize the printing head to be attached to the shuttle frame so that the adjustment in the assembly or the maintenance can be done by every unit, and such a kind of a device has been requested.
Conventionally, such unitization of the printing head was partially carried out unintentionally. Structurally, a dot printer having a single printing head is a fundamental example, and the movement of the printing head to column and line directions constructs requested dot letters by means of driving one or more printing wires at predetermined positions by the single printing head. In such a fundamental head conventionally offered therein is a unitized device of the electromagnetic actuator and the printing wire. However, in the shuttle type dot line printer such a device has never been provided that, when a plurality of printing wires are assembled to the shuttle frame, the individual printing head block is composed as a complete assembly unit; in other words, a unit completely unitized by both the electromagnetic actuator and the printing wire and perfectly adjusted as a complete assembly. Furthermore, this complete assembly unit is designed to be small in size and light in weight.
Especially, in the prior art device, such a thought has been predominant that the components of the respective printing heads are attached to a base plate being received by the shuttle frame. Even if each of the printing heads is unitized, every printing head is thought to have a separate base plate to attach the necessary component thereto. This base plate increases the weight of the printing head or the shuttle frame without question, which cannot be ignored. Accordingly, in the prior art device, despite troublesome adjustments and maintenances, it is a general thought that the shuttle frame receives the respective components as the base plate in order to have a light weight device, and there has been a tendency that every printing head avoids unitization.
Thus, in the prior art device, it was difficult to realize a dot line printer with higher production efficiency and low cost.